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dtb_419

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## Homework Statement

I want to calculate the horizontal deflections at joints A and F (using Virtual Work method taught in Structural Engineering). Cross-Sectional Area (A) and E values are provided in the problem, and the attachment has all relevant dimensions and applied loads.

## Homework Equations

Deflection is 1[k](Δ)=∑(Virtual Force/AE)

## The Attempt at a Solution

So far in class, Virtual Work problems have involved using the Unit Load Method (a hypothetical 1 kip load that can be used to calculate deflection from its effect on a given structure).

The general method (as I understand it, in a truss structure) is this:

1. Solve all member forces.

2. Organize all information (member length in inches, member force, cross-sec area, and

*MEMBER FORCE FROM UNIT LOADING*into a table.

3. Summation of Virtual Forces from table plugged into Deflection Equation from Virtual Work.

Step 1. I've already done myself (joint method), and Step 3. is a matter of plugging in known data from Step 2. No questions there.

Step 2. is where my question is.

This particular question wants horizontal deflections at A and also F. What I think I should do is introduce a horizontal 1 kip load at each of the respective joints, and repeat the joint analysis to reflect this change from the unit load. But in what direction (sign convention) should they be introduced? Should I introduce a horizontal 1 kip load at EACH joint, or only the requested joints?

Some problems I've seen introduce the unit load at only the requested joint, and recalculate all other member forces to adjust for that change (which is what I'm leaning towards doing), but others introduce the unit load immediately, without taking initial member forces. This is confusing, and so I'm asking for a clarification in procedure.

No numbers are necessary. Thanks everyone!

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